As is well known, Leonardo defines painting as the "daughter of nature". His observation of nature, his fascination with every living thing that surrounded him was the main source of his drawings. His entire life was dedicated to investigating and trying to understand the laws of nature. Nature is observed, studied and depicted in all its forms. In fact, Leonardo constantly aims at reproducing every element of nature: animals, flowers, fruits, birds and also, a female smile, the throbbing of the hearth or - following a series of examples - the intricate plait of Renaissance hairdos. All these elements have in common the uninterrupted flow of the secret of life.